Computers and other devices requiring a visual interface often use liquid crystal displays (LCDs) to display data. Recently, color LCDs utilizing active matrix and passive matrix technologies have become commonplace. Display systems employing either of these technologies require light from a backlight to generate the colors displayed to a user. In such systems, the backlight generates an image plane of light beneath the LCD, which in turn generates the color display.
As is known in the art, LCD technologies transmit only a small portion of the light generated by the backlight. The intensity of display systems incorporating these technologies therefore depend largely upon the intensity of the backlight. Therefore, to have a high-intensity image transmitted to the user, the backlight must be substantially brighter than a desired viewer intensity.
The need for a high-intensity backlight is hightened when one considers that special filters are often applied to the front of LCD displays to prevent "washing out" of the display where large amounts of ambient light are present such as outdoors in high-intensity, bright sun light. Such filters further reduce the amount of light transmitted to the user thereby necessitating very bright backlights for such applications.
Unfortunately, such high-intensity backlights generate a large amount of heat which oftentimes causes problems with the operation of the LCDs. As is known in the art, LCDs operate over a relatively narrow range of operating temperatures. If the LCDs are operated outside of this range, they may completely and irreversibly fail. Consequently, any high-intensity backlight contemplated for use within a LCD must not heat the LCD outside of its narrow range of operation.
Furthermore, a backlight must be lightweight and possess a low profile. Since many present day applications of LCDs are mobile, portable, lightweight, and low profile are very desirable attributes of a backlight for a display. Additionally, a backlight must have a long lifetime and provide a uniform emission of light across its display surface. Finally, a backlight must emit light in wavelengths required by the LCDs employed in the display and provide that light to the LCDs.
In summary, desirable backlights for display systems should be cool in operation but output high-intensity light, have a low profile, a low mass, a long lifetime, have a high uniformity and must emit light in the required wavelengths.
Prior art backlights and related technologies do not generally offer all of these desirable attributes. Specifically, U.S. Pat. No. 4,479,328 discloses a backlight having a serpentine fluorescent tube nested in a shaped reflector. Light emitted from the fluorescent tube is both emitted to an image plane and the shaped reflector. The reflector reflects a portion of the light to the image plane in such a manner that a very bright and uniform image is formed at the image plane. As stated by the patentees there, fiber optic backlights are very expensive, very bulky, and have a high power consumption. Nevertheless, the prior art is replete with many such devices.
U.S. Pat. No. 5,037,172 issued to Hekman et al. on Aug. 6, 1991 for a Fiber Optic Device with a Reflective Notch Coupler discloses a structure and method for manufacturing a reflective notch coupler for an optical fiber. The coupler is formed in an optical fiber by a pair of angled surfaces extending from the cladding of the optical fiber and meeting in the fiber's core to form an indentation in the fiber. One of the surfaces is reflectively coated and couples light into and out of the core of the optical fiber. When light traverses the core of the fiber and encounters the reflective surface, it is reflected out of the fiber in a direction substantially perpendicular to the fiber. Variations of such a side-emitting optical fiber have been used as an illumination device in a variety of displays.
U.S. Pat. No. 4,845,596 describes an illumination device for producing illumination of a surface, comprising several parallel optical conductors which are placed above an optically reflecting surface, and whose reflecting outside sheath is removed locally at least in such a way that the light thereby emerging from the optical conductor is reflected by the reflecting surface to the surface to be illuminated. The optical conductors are spaced at such intervals and at such a distance above the reflecting surface that the light reflected by the reflecting surface can reach the surface to be illuminated on the other side of the optical conductors through the space between the optical conductors in such a way that a uniform illumination of the surface is obtained.
U.S. Pat. No. 4,234,907 discloses a light emitting fabric in which optical fibers are part of the fabric weave, replacing some of the threaded fibers. The fabric uniformly illuminates light which is accordingly decorated. The individual optical fibers are gathered into a bundle at one end of the fabric and illuminated by a light source. Light traveling through the fibers is emitted in small amounts throughout the lengths thereof through small scratches that pierce the outer coating. Uniformity and intensity of the light are enhanced by providing a reflective coating on the non-illuminated ends of the optical fibers.
U.S. Pat. No. 5,187,765 discloses a light emitting panel backlighted by an optical fiber assembly in which individual optical fibers are positioned in parallel across the bottom of a frame and transverse notches are scored in the cladding so as to permit lateral emissions of light along the length of the fibers. In a preferred embodiment, the lateral emissions are projected onto a diffusing plate mounted in the top of the frame to provide uniform illumination throughout the entire area of the light emitting panel. Increased light throughput is obtained by inducing air flow at the end of the optical fiber bundle to keep the end surface cool by removing the heat from light energy impinging upon the end.
U.S. Pat. No. 5,097,396 issued to Meyers on Mar. 17, 1992 for a Fiber Optic Backlighting Panel describes a fiber optic panel for providing backlighting in devices such as rubber keypads, membrane switches, liquid crystal displays, rigid panels and the like. The fiber optic panel comprises a light source for emitting light and a fiber optic cable which transmits the light to a plurality of locations throughout the device. The fiber optic cable includes a plurality of optical fibers, each of which individually terminates at one of a plurality of locations to illuminate that location or, alternatively at spaced locations throughout the device to illuminate a region of the device uniformly.
U.S. Pat. No. 5,307,245 extends the teaching of the above U.S. Pat. No. 5,097,396 fiber optic panel so as to provide uniform and increased background illumination in backlight devices. The fiber optic panel includes a light source and a layer of optical fibers arranged adjacent to each other, which transmit light to different locations throughout the device, thereby providing efficient background illumination. The optical fibers are selectively terminated at locations by forming a series of angular cuts through the layer of optical fibers in a zig-zag pattern. The zig-zag pattern extends across the length and width of the panel such that each optical fiber is cut only once so as to provide increased and constant illumination throughout the device. In a specific embodiment, for application with liquid crystal displays, a layer of foam is used to diffuse the light to further provide uniform illumination.
A Fiber Optic Light Emitting Panel was disclosed in U.S. Pat. No. 5,568,964 which included one or more light emitting layers that are sealed along side edges and/or an end edge. A thin film, sheet or coating is applied to one or both sides of the light emitting portions of the panel assembly. If a more brighter and/or more uniform emission of light is desired, two or more panels may be joined together. Typical applications of such a panel include backlighting of liquid crystal displays, membrane switches, alphanumeric displays and the like.
A Light Emitting Optical Fiber Assembly was disclosed in U.S. Pat. No. 4,519,017 wherein the light emitting optical fiber assemblies include light emitting panels that employ a nonwoven geometric grid of light emitting optical fibers. The fibers are arranged so as to permit air to pass through or define apertures providing access through the panel. The nonwoven grids can be arranged to permit the panels to be cut or sectioned without losing all light emitting capacity. Panels are provided with optical fibers that have been encapsulated with light transmitting laminate, and the laminate is imparted with a light scattering formulation which permits light to be emitted from the encapsulated layer.
U.S. Pat. No. 5,042,892 for a Fiber Optic Light Panel discloses a light emitting panel formed by a single layer of parallel and contiguously arranged, clad optical fibers supplied with light from a source at one end of the panel. The fibers are cemented together and the cladding is removed from the light emitting surface of the panel. In a particular embodiment, each fiber is looped at the end of the panel remote from the source of light so that both ends of each fiber is connected to the source of light.
A Fiber Optic Display System Utilizing a Dual Light Source was described in U.S. Pat. No. 5,307,057 issued to Cook et al. on Apr. 26, 1994. There, a fiber optic display sign having a plurality of magnetically actuable indicator elements each having associated therewith at least two fiber optic cables for transmitting light. Each of the fiber optic cables has an end face for emitting light which terminates in an indicator element, and an end face for receiving light which is positioned in close proximity with the other light receiving end faces to form a light receiving surface. A light source assembly is movably related to the light receiving surface and includes a primary light and a secondary light.
U.S. Pat. No. 5,329,388 discloses a liquid crystal display system constructed from a plurality of liquid crystal display cells stacked one on top of another. A light guide adapted to transmit light only in a direction perpendicular to the display surfaces of the liquid crystal display cells, is interposed between the first liquid crystal display cells nearest to an observer and the second liquid crystal display disposed behind the first liquid crystal display cell. Because of the provision of the light guide, the images formed on the second and third liquid crystal display cells are focused through the light guide onto the rear surface of the first liquid crystal display cell, viewed from the direction of the observer. The light guide is a sheet of optical fibers or a stack of sheet like members separated by reflection films, the plane of which are perpendicular to the plane of the display.
U.S. Pat. No. 5,181,130 describes a fiber optic faceplate liquid crystal display which includes a layer of liquid crystal material, a thin transparent layer, one or more polarizers, and a fiber optic faceplate. The fiber optic faceplate serves to allow ambient light from a much wider range of incident angles to illuminate the LCD than would be the case with prior art LCDs, and allows the viewer to position himself so as to avoid front surface glare and still see the display brightly illuminated, even in difficult lighting situations.
Yet while a number of prior-art systems and techniques exist for providing a backlight for liquid crystal displays, each of the prior art systems and techniques suffer from one or more infirmities It is desirable therefore, and a continuing need exists in the art for backlighting systems and techniques which are cool in operation, output high-intensity light, have a low profile, a low mass, a long lifetime, and have a high uniformity while emitting light in the required wavelengths.